Many yarns, particularly spun yarns, consist of a central core of relatively tightly-intermeshed fibers, surrounded by a region of progressively less-dense fibers protruding from the core. The protruding fibers are termed yarn hairiness. The amount of hairiness is important to both textile operations as well as fabric appearance. In operations such as air jet weaving, the aerodynamics of the yarn influence the amount of energy necessary to move the yarn. The amount of hairiness also contributes to the quality of the yarn, and the final appearance of fabric made from the yarn. Thus, knowledge of yarn hairiness is important.
One of the current methods used to measure yarn hairiness is embodied in the Zweigle hairiness tester. The Zweigle tester has a lamp which shines a light only on yarn fibers which protrude above the yarn core. The fiber images are projected onto twelve photo transistors, each of which is a different height from the bottom of the yarn core. The number of fibers projecting to each of the twelve heights is counted. A problem with this approach is that the device does not account for or measure the yarn core. Also, the actual length of fibers must be measured outward from the periphery of the yarn core. However, since Zweigle tester does not determine the core thickness, the actual fiber lengths are not measured.
The second basic method of yarn testing is embodied in the Uster Tester 3. This device shines light on the yarn. The device has an aperture in front of the detector whose purpose is to block any light that would move directly from the light source to the receiver. The optical receiver, then, picks up only light that is scattered by the yarn. The detector transforms the light received into proportional electrical signals for evaluation. This system, however, directly measures only the light-scattering properties of yarn--there is no direct measurement of hairiness. Any factors which could affect the light scattering capability of the yarn, including the density of the core, the thickness of the fibers, and the fiber reflectivity, would all contribute to the measured value, despite the fact that these factors do not contribute to hairiness. Accordingly, this test is qualitative. Clearly, the test does not result in the actual determination of hairiness, the length of the hairs, or the diameter of the yarn core.